PLL using 4046 – Phase Locked Loop

CD4046 is a PLL or phase lock loop, it mainly consists of a VCO and phase comparators. This is a component in FM demodulation and modulation.

Mixed and Interface Circuits

PLL using 4046

It is used in a closed loop control to maintain a stable frequency. The Circuit above is good for learning the full use of a small Dual Trace Scope. The Circuit has both Analog and Digital areas and is a part of communication.

Read the pages above for building more Knowledge on PLL

LM311 Square Triangle Oscillator for PWM

LM311 is a comparator, It operates from single 5V supply or dual supplies,input current 150 nA, 50 V-50 mA output drive capability. TTL-CMOS compatible output.

Even LM324  used as a  comparator Water Level Indicator with Reed Relays

The Output is open collector so it can sink current but cannot source, a totem pole output can source and sink. In this Circuit R2 is the source or pull-up.

LM311 Square Triangle Oscillator for PWM

The Output being high or low depends on which input is more dominant or positive. If + or non-inverting input is more positive than the – inverting input then output of LM311 is high impedance or high Z as output transistor of LM311 is turned off, but output goes high due to R2 pull-up 1K, so you can apply a load of 10K and above for source. When the – input or inverting input is more positive, output goes Low as transistor turns on, now a current of upto 50mA can sink here, a LED or Relay can be driven.

Mixed Circuits Analog with Digital

On turn on C2 capacitor is discharged and pin 3 the inverting input is at a lower potential than pin 2 the non-inverting which is at 2.5V. Hence output goes high and C2 starts charging thru R5, When C2 charges a little beyond 2.5V pin 3 is more dominant and output goes low now, this slowly discharges the C2 bringing the voltage at pin 3 again below 2.5V so output goes high again. This process goes on, hence it oscillates. The charging and discharging is at the rate of R5 * C2 approx. , R3 serves as hysteresis or feedback to ensure clean turn on and off.

Monostable Multivibrator CD4538

CD4538 is a dual Monostable Multivibrator. When you trigger the chip the output sends off one single pulse or one high-low event.

Mixed Circuits Analog with Digital

The T+ pin 4 of U1a is the positive edge trigger or raising edge trigger input, the T- pin 5 is falling edge or negative edge trigger input. Now see the image of the single pulse above which shows both the edges, If this is the input pulse at pin 5 then the falling edge turns the output pin 6 from low to high, this output remains high for time T = R2 * C1 and then goes low again, The output Q at pin 6 also looks like the image of pulse above.
Monostable Multivibrator CD4538

The Output pin 7 is the complementary state of pin 6, it is the reverse state or inverted form of pin 6 output.

Now why is a slope shown in the edges, this i have exaggerated a bit so that it can be explained. But then there is a slight slope due to gate input and output capacitance.

In fact if you had a wire or twisted track coming to the input and the R2C1 was in nano seconds, then you would see a ringing at the edges, a tiny peak or spike, which will have giga hertz frequency components, in fact a square way may be many sine waves put together, this you know from a spectrum analyzer.

Two Stage Sequential Timer

CD4538B can give an output with pulse width of 1uS and above. 74HC4538 gives 120nS to 60 Seconds pulses. The above circuit produces a pulse of width T = R3 * C2 after a delay of T = R2 * C1. Some Chips formula is T = 0.7 * R * C .

Fixed frequency Variable duty cycle with 555

This circuit is based on a very old application note from exar, in this the frequency is fixed by IC1 and IC2 -P1 controls the duty cycle. you need to compute the R and C values to get what you need,  LM555 data sheet.

You have to study the circuit and do something more innovative perhaps, just copying is ok for learning but it will get you nowhere, so learn and then innovate, the eagle circuit is given below so you can learn by editing it, also design a PCB with it, and you can even make a PCB at home to learn, but it is always good to get PCBs done by a PCB vendor, but you should understand his problems, then you will design well, so make a few PCBs.

Fixed frequency Variable duty cycle with 555

Edit the circuit eagle cad file